1. Field of the Invention
The present invention relates to an ink jet head, and more particularly to a filter for removing the foreign matter and air bubbles in the ink, an ink jet head having the filter, and an ink jet recording apparatus using the ink jet head.
2. Background Art
Generally, an ink jet head discharges the ink by applying a pressure to the ink introduced through an ink inlet opening by driving a piezoelectric element. In this ink jet head, if the foreign matter exists in the supplied ink, an ink flow passage or nozzle may be clogged, causing a discharge failure. Also, when air bubbles residing in the ink impede the flow of the ink, or the pressure applied by the piezoelectric element is absorbed, a discharge failure is caused. Therefore, a filter for removing the foreign matter or air bubbles in the ink through a plurality of minute holes is usually mounted on the way to the ink supply passage.
This filter conventionally employs a texture woven from the fiber as the filter pores. When the ink passes through the filter pores, the foreign matter and air bubbles are removed. However, since the filter of this structure does not allow the use of too thin fiber, the aperture ratio is reduced if the filter pores are smaller. Consequently, there is a problem that a pressure loss in flowing the ink is increased, degrading the discharge performance. (Here, the aperture ratio of the filter is a ratio of sum total area of the filter pores in proportion to the area of the whole filter portion.)
Also, a method for increasing the aperture ratio was disclosed in which a nickel plate formed with round pores by electro-forming is employed as the filter. (refer to JP-A-11-291514) The aperture ratio of the filter produced by this method is about 30%, and the filter having less influence on the pressure loss in the flow of the ink can be produced.
However, when the nozzle diameter of a head is reduced along with the higher definition of print in recent years, there is a need for reducing the diameter of filter pore. The electro-forming method may not treat this need in some cases, due to a limited resolution of patterning the resist. Also, there was a problem that nickel was corroded when the discharged liquid was a solvent or corrosive liquid.
Thus, a filter portion is formed with the concave portions of predetermined shape by etching the surface and back face, employing a corrosion-resistant material for the discharge liquid, the through holes being provided in the areas where the concave portions overlap. However, the filter member has a pattern for positioning with other parts, in addition to the filter portion. If due to a dispersion in the etching progress rate within the part face, the timing when the portion of through hole is penetrated is varied, there is a distribution in the flow of etchant, amplifying the distribution of etching progress rate. Consequently, the filter portion has a lower precision of through hole, and does not operate as the filter.